A "standard leak" is a calibration standard used to set leak detection equipment. The word "leak" denotes a very low and constant flow rate of gas. Standard leaks may be of several designs, but they generally consist of a pressurized chamber discharging through a capillary or membrane. Rates generally range from 1.times.10.sup.-4 to 1.times.10.sup.-10 atmosphere cubic centimeters/second with the rate remaining essentially constant for months or even years at a time.
The standard leak itself must be periodically recalibrated because the degree to which the leak rate decreases with time varies depending upon the conditions of use and storage.
Existing calibration methods and devices for standard leaks include such inaccurate and awkward principles as bubbling in water in which, a 1.times.10.sup.-8 atmosphere cubic centimeters/second leak produces one bubble in 667 hours or moving a slug of liquid through a tiny capillary tube. More sophisticated systems which use vacuum systems and mass spectrometers or similar hardware are expensive to purchase and difficult to operate. Atmospheric pressure calibrators exist which measure volume displacement with small pistons which are manipulated through seals by the operator. Seals are required to separate the measured volume from fluctuations in barometric pressure. Unfortunately, sliding seals tend to develop leaks as large or larger than the leak rates being measured. Therefore, it can be seen that a more accurate and reliable device for measuring the flow rate produced by standard leaks for the purpose of calibration is needed.
Accordingly, it is an object of this invention to provide a relatively simple closed system device for measuring the flow rate produced by standard leaks for the purpose of calibration.
Another object of this invention is to provide a device which is simple to operate, totally sealed from the atmosphere, and which requires no vacuum system for its operation.
Still another object of this invention is to provide a system which has no seals that are readily subject to leakage due to the seal moving relative to a sealing surface.
Other objects and advantages of this invention will be obvious to those skilled in this art.